Interactions between large molecules pose a puzzle for reference quantum mechanical methods
It is shown that CCSD(T) and DMC interaction energies are not consistent for a set of polarizable supramolecules, indicating that more caution is required when aiming at reproducible non-covalent interactions between extended molecules.
Abstract
<jats:title>Abstract</jats:title><jats:p>Quantum-mechanical methods are used for understanding molecular interactions throughout the natural sciences. Quantum diffusion Monte Carlo (DMC) and coupled cluster with single, double, and perturbative triple excitations [CCSD(T)] are state-of-the-art trusted wavefunction methods that have been shown to yield accurate interaction energies for small organic molecules. These methods provide valuable reference information for widely-used semi-empirical and machine learning potentials, especially where experimental information is scarce. However, agreement for systems beyond small molecules is a crucial remaining milestone for cementing the benchmark accuracy of these methods. We show that CCSD(T) and DMC interaction energies are not consistent for a set of polarizable supramolecules. Whilst there is agreement for some of the complexes, in a few key systems disagreements of up to 8 kcal mol<jats:sup>−1</jats:sup> remain. These findings thus indicate that more caution is required when aiming at reproducible non-covalent interactions between extended molecules.</jats:p>